Folding machines for folding large paper sheets have been proposed in which the paper sheet is fed to a folding system having folding means, for example belts therein, operable in respectively different directions of rotation. A feed roller pair is located ahead of the folding system. The folding system has at least two endless, driven folding belts, wrapped about respective turn-around rollers, the axes of which are in the same plane. A third, endless belt is spaced from the aforementioned belts by a small distance to form a folding gap. A control system is provided for controlling the respective direction of rotation of the belts.
Folding machines of this type are used for example to fold large machine drawings, architectural layouts and the like, and have a substantial structural length. This large space requirement is a disadvantage.
The German Published Patent Application 2 227 582, (Werthebach) describes an arrangement for folding paper sheets utilizing a plurality of folding rollers which, by change in the direction of rotation, cause a sheet fed thereto to be folded. Close to the inlet opening, the paper sheet is caused to form a loop which is gripped by the folding rollers, and is then formed to make a fold. Microswitches are provided which sense the presence of a sheet in a folding gap, and, upon sensing the sheet, cause a change in the direction of rotation of the folding rollers. The folding program, and the position of the folds, that is, the folding length with respect to the longitudinal direction of the sheet, is always the same and cannot be changed.
Published European Application 0 156 326, (Isermann et al.) describes a horizontal folding machine for folding sheets which, in order to measure the longitudinal extent of the sheet, has a measuring roller associated therewith. The measuring roller is coupled to a pulse source. The trailing edge of the sheet is sensed by a sensor remote from the folding mechanisms. Such a structure for handling large sheets, is space-consuming and the folds cannot be selectively predetermined.